Mud Valves are a kind of valve which are used primarily as drain valves for large containers of liquid, such as the various tanks used in sewage treatment plants or the like. They are mounted flat upon one surface of a tank for holding fluids, typically inside the tank on the bottom, and are usually used to prevent or enable a liquid in the tank from draining into pipes.
Mud valves have long been known to the art. They have the advantage of being inexpensive and simple to operate, and, since they mount within the tank, can shut off the tank and allow removal and maintenance of the pipes leading to the tank without loss of liquid. Despite these advantages, mud valves have been declining in popularity in recent years.
In all figures, identical reference numbers refer to identical features.
The prior art mud valve, as illustrated in FIG. 3, has a circular frame 2 mounting flat upon the bottom of a tank 13 over an opening in the bottom. The center of the frame 2 is open, forming the valve opening 14, through which liquids may pass. The frame 2 has a valve seat 32 surrounding the valve opening 14 in the middle of the frame 2. A horseshoe-shaped yoke 1 is attached to the frame, typically by means of bolts 11, and extends above the frame, and perpendicular to it, up into the tank. A stem 3 extends through the yoke 6 above the center of the valve opening 14. The stem is free to rotate around its long axis. The bottom end of the stem extends into the center of horizontal circular plug 4. The plug 4 has a portion around its bottom edge which acts as a plug seat 31, matching the valve seat 32 on the frame 2. The plug 4 usually has flanges 6 which ride along the sides of the yoke 1 to prevent the plug 4 from turning relative to the yoke. The top end of the stem 3 is adapted to mate with a valve handle, perhaps by being attached to a hex-shaped cap 5 which will fit a wrench or the like.
In the "non-rising-stem" type mud valves shown in all of the figures, the portion 10 of the stem 3 which passes through the yoke 1 is not threaded, but the stem is threaded along its lower portion 10 where it mates with an extended part 7 of the plug which is threaded to match the stem. The stem is held into the yoke by a cap 9 bolted to the yoke 1. As the stem is turned, it remains in position relative to the yoke, but the plug is drawn vertically up or down by the threads on the stem, carrying the plug seat toward or away from the valve seat, and thus opening or closing the valve.
In an alternative "rising stem" design (not shown), the portion of the stem which passes through the yoke is threaded, but the plug itself is not threaded, so that the stem may turn freely within the plug (while remaining affixed to the plug for vertical movement). As the stem rises and falls, the plug is drawn up or down. It will be understood by one skilled in the art that this variation does not affect the operation of the seal, which is the focus of this invention.
The plug seat-to-valve seat seal, as shown in FIG. 4, has traditionally been nothing more than a flat seat area 42 upon which the a portion of the plug 41 is pressed. An improvement in this (FIG. 3) has the plug formed with a seat area 31 which tapers at 45.degree., mating with a recessed seat area 32 in the frame which also is tapered at 45.degree.. In all prior art designs of which the inventor is aware, both the valve seat and plug seat areas are made of a nonresilient material such as bronze or the like, for long wear.
This has caused mud valves to develop a reputation for leakage, as it is difficult to impossible to attain a bubble-tight seal with non-resilient seats and current valve designs.
With the increasing strictness of environmental controls, it has become more important to be able to shut off valves without leakage. Designers have been forced by this to abandon the simple, inexpensive mud valve in favor of more expensive and complicated in-line valves such as butterfly, plug or gate valves. These valves are capable of bubble-tight seals, but they must mount in piping, which means that the tank itself cannot be sealed off, as it could with an in-tank mud valve.
It is thus an object of this invention to provide a mud valve which is capable of a bubble-tight seal.
The prior art mud valves, whether flat sealed or 45 degree sealed, are also strictly unidirectional--that is, they seal against pressure from within the tank, but not against back pressure from the pipe.
It is thus a further object of the invention to provide a mud valve which is capable of a bidirectional seal.
Waterman Industries, Inc, of Exeter, Calif., has attempted to improve the valve and provide a bubble-tight seal by setting a resilient O-ring into a slot in the valve seat. This has the disadvantage of O-ring wear, makes the valve more susceptible to dirt in the seal, and adds the necessity of adding an appropriately sized slot into the seat, which greatly increases the expense of manufacturing the valve.
It is thus a further object of the invention to provide a mud valve which does not use O-rings or other separate inset seal elements.
Finally, the prior art mud valves with their nonresilient seals and flat or 45 degree seats, tended to require relatively high torques to effectuate the best seal of which they were capable.
It is a further object of the invention to provide a mud valve which will effect a bubble-tight seal with relatively low torque required.